There is a need for water-based adhesive compositions to provide high strength, bonded wood composites that would be suitable for use in exterior applications, particularly when laminated at room temperature. Another hindrance to the use of water-based systems is that most polymer/isocyanate adhesive compositions have very limited pot lives of less than about 30 minutes. In the past, self-crosslinking vinyl and acrylic polymers and the combinations of these polymers with polyisocyanates have been used in making wood composites, but these either fell short of the required bond characteristics or were difficult to employ because of the relatively short pot life or toxicity shortcomings.
U.S. Pat. No. 3,632,789 discloses a process for the production of coatings based on reaction products of polyisocyanates with copolymers containing hydroxyl groups which have been prepared by polymerization of the monomers in an organic liquid (which does not react with isocyanates in the presence of the soluble polymer) as the insoluble copolymer dispersed in the organic liquid.
U.S. Pat. No. 3,931,088 discloses an adhesive composition comprising: (1) a member selected from the group consisting of an aqueous solution of polyvinyl alcohol, an aqueous emulsion of vinyl acetate polymer and an aqueous latex of butadiene polymer, and
(2) a hydrophobic solution of an isocyanate compound or polymer.
U.S. Pat. No. 4,191,833 discloses ethylenically unsaturated blocked aromatic di-isocyanates which readily polymerize to form homopolymers and interpolymers with copolymerizable vinylidene monomers. Polymers can be prepared via emulsion polymerization and exhibit excellent stability to hydrolysis when stored in latex form.
U.S. Pat. No. 4,215,023 discloses a thermosetting coating composition of a urethane polymer having film-forming constituents of an organic polyisocyanate, a polymer of polymerized ethylenically unsaturated monomer units which contains pendant hydroxyl-containing groups and a hydroxyl-containing alkyd plasticizer.
U.S. Pat. No. 4,268,641 discloses copolymers of acrylic acid and nonionic surfactant acrylates useful as thickening agents for both aqueous solutions and water/liquid hydrocarbon emulsions.
U S. Pat. No. 4,295,910 discloses a lamination process for the lamination of a vinyl film to a cellulosic substrate, such as a wood product, e.g., particleboard wherein grain swelling of the substrate is avoided. The process involves coating the wood product substrate with an organic polyisocyanate having at least two active isocyanate groups per molecule as a primer coat, and thereafter applying a vinyl acetate-ethylene copolymer emulsion adhesive to the primed substrate to form an interlaminate adhesive layer. A vinyl polymeric film is then applied to the adhesive coated substrate to form a permanently bonded laminate of the substrate and of the film.
U.S. Pat. No. 4,340,682 discloses a curable urethane adhesive composition having a high green strength consisting essentially of a mixture of an isocyanate terminated ricinoleate prepolymer and chlorinated polyvinyl chloride curable by reaction with compounds having reactive hydrogen such as water, amines, polyols, urethanes, ureas and the like.
U.S. Pat. No. 4,396,738 discloses aqueous adhesive and coating compositions comprising:
(1) an aqueous emulsion or dispersion of a polymer or interpolymer of one or more vinyl monomers such as an emulsion of a copolymer of vinyl acetate and butyl acrylate; and
(2) an aqueous emulsion or dispersion of a polyisocyanate which has at least partially reacted with an alcohol having the formula ROH wherein R is a hydrocarbon radical having at least one carbon atom and wherein the dispersion or emulsion (2) is stabilized with a combined surfactant and alcohol, having the formula R.sup.1 OH wherein R.sup.1 is a hydrocarbon radical having at least one carbon atom as described.
U.S. Pat. No. 4,433,095 discloses aqueous adhesives which are based on water-dispersible polymers and which contain water-dispersible polyisocyanate preparations having an average NCO-functionality of at least 2.2, which in addition to an aromatic polyisocyanate or a mixture of aromatic polyisocyanates, contain a quantity of emulsifiers sufficient to guarantee the dispersibility of the polyisocyanates as additives capable of improving the bonding properties of these adhesives.
U.S. Pat. No. 4,476,276 discloses a sealing composition prepared by reacting water soluble polyurethane prepolymer with water containing latex to provide a gelled viscous mass which will cure to a cross-linked latex-reinforced gel capable of preventing or inhibiting leakage in various structures, when applied at the site of the leakage in the viscous state.
U S. Pat. No. 4,491,646 discloses an aqueous latex adhesive composition of the type having an aqueous latex admixture with an organic solvent-dispersed multi-isocyanate cross-linking agent and a thickener. The improvement for a room temperature curable adhesive composition having improved water-resistance comprises the curable ingredients consisting essentially of an aqueous hydroxyl functional acrylic latex which contains hydroxyl groups as the only isocyanate reactive functionality and the multi-isocyanate cross-linking agent.
U.S. Pat. No. 4,609,690 discloses an aqueous latex adhesive composition which is an aqueous latex admixture with a water dispersible multi-isocyanate cross-linking agent and a thickener. The improvement for a room temperature curable adhesive composition having improved water-resistance comprises the curable ingredients consisting essentially of an aqueous hydroxyl functional latex which contains hydroxyl groups as its only isocyanate reactive functionality and the multi-isocyanate cross-linking agent. The cross-linking agent is a water dispersible or water dispersed multi-isocyanate and preferably is a multi-isocyanate which has undergone partial reaction of some of its isocyanate groups with a hydrophobic monohydroxy alcohol.
U.S. Pat. No. 4,663,377 discloses a polyisocyanate preparation dispersible in water and having an average NCO functionality of about 2.0 to 3.5, which contains:
(a) an aliphatic polyisocyanate or a mixture of aliphatic polyisocyanates; and
(b) a quantity of an emulsifier sufficient to ensure the dispersibility of the polyisocyanates.
This polyisocyanate preparation is used as an additive for aqueous adhesives based on polymers dispersed in water.
U.S. Pat. No. 4,767,816 discloses an aqueous copolymer emulsion comprising a copolymer consisting essentially of vinyl chloride, ethylene, and up to 10 wt % hydroxyalkyl (meth)acrylate colloidally dispersed in an aqueous medium. The latexes can be used as a saturant binder for filter stock substrates. Optionally, the latex can be cross-linked with melamine-formaldehyde, phenol-formaldehyde, urea-formaldehyde, or reactive polymeric isocyanates to enhance the strength and other mechanical properties of the treated filter.
J57/85,871 discloses an adhesive composition comprising an emulsion of ethylene/vinyl acetate copolymer containing polyvinyl alcohol and an adduct of di-isocyanate prepolymer with a polyhydric alcohol.